1. Field of the Invention
The present invention relates to a multilayer ceramic circuit board and a method for manufacturing the multilayer ceramic circuit board. More particularly, the invention relates to a multilayer ceramic circuit board which is suitable for use when protruding portions are provided on the surface of the multilayer ceramic circuit board, and a method for manufacturing the multilayer ceramic circuit board.
2. Description of the Related Art
FIG. 8 shows an example of a multilayer ceramic circuit board 101 according to the related art. The multilayer ceramic circuit board 101 is formed by stacking a plurality of ceramic wiring layers 102. A protruding portion 106 is disposed on the surface of the multilayer ceramic circuit board 101 so that contacts 107, such as ones shown in FIG. 8, and a quartz oscillator 108, such as one shown in FIG. 9, can be mounted on the protruding portion 106.
For example, two widely used methods for forming the protruding portion 106 according to the related art are mentioned below. In a first method, as shown in FIG. 8, the protruding portion 106 is formed on the surface of the multilayer ceramic circuit board 101 by stacking a plurality of ceramic sheets 122 that are smaller than the ceramic wiring layers 102.
In a second method, as shown in FIG. 10, a heat-resistant, constraining green sheet (hereinafter referred to as “recessed constraining sheet”) 131 having recessed portions 131a at positions facing protrusion portions 106 and a planar heat-resistant, constraining green sheet (hereinafter referred to as “planar constraining sheet”) 130 are prepared. The recessed constraining sheet 131 is allowed to abut on a first surface of the unfired multilayer ceramic circuit board 101, the planar constraining sheet 130 is allowed to abut on a second surface of the unfired multilayer ceramic circuit board 101, and then the multilayer ceramic circuit board 101 is fired under pressure. During the firing process under pressure, the multilayer ceramic circuit board 101 is constrained by the recessed constraining sheet 131 and the planar constraining sheet 130. Consequently, when the firing process under pressure is completed, as shown in FIGS. 9 and 11, the surface of the multilayer ceramic circuit board 101 swells out into the recessed portions 131a of the recessed constraining sheet 131, and thus protruding portions 106 are formed on the surface of the multilayer ceramic circuit board 101.
In the first method for forming the protruding portion 106, however, as shown in FIG. 8, since the side of the protruding portion 106 is steep, it is not possible to dispose a wiring pattern continuously so as to extend from the region provided with the protruding portion 106 to the region not provided with the protruding portion 106 via the side of the protruding portion 106, which is a problem.
Furthermore, in the second method for forming the protruding portions 106, the protruding portions 106 are protruded by pressure deformation. There is a limit to the amount of deformation caused by the pressure deformation. Therefore, although a protruding portion 106 can be formed appropriately when the protruding portion 106 is small in area as shown in FIG. 9, pressure deformation cannot be performed appropriately when the protruding portion 106 that is large in area is formed as shown in FIG. 12. Consequently, in the second method for forming the protruding portions 106, the surface flatness of the protruding portion-formed surface decreases. When contacts 107 shown in FIG. 12 or quartz oscillators (not shown) are disposed on the protruding portion-formed surface, a difference in height may occur in the contacts 107 or the quartz oscillators, which is a problem.